Photomasks are widely used in the semiconductor industry during photolithography steps of semiconductor processing technologies. Photomask plates generally comprise a quartz blank having a patterned metal layer on one surface. Both surfaces of photomask plates are often protected from dust particles through the use of pellicle films. Typically, the pellicle films are stretched across a pellicle frame which is adhered to the surface of the photomask plate. The pellicle film can then keep dust away from the photomask plate surface without affecting the function of the photomask plate. During use, pellicle films can degrade, be punctured or otherwise be damaged while the photomask plate remains usable. Because it is expensive to replace photomask plates, it is desirable to remove the pellicle frame from the photomask plate and attach a new pellicle frame (this is sometimes referred to as re-pelling the photomask plate).
A wide variety of adhesive materials can be used to adhere a pellicle frame to a photomask plate. However, pellicle frames are increasingly adhered to photomask plates using a solid adhesive gasket (SAG) adhesive material. The solid adhesive gasket is glue-like material that hardens at ambient temperatures but melts when heated to higher temperature levels, for example above 95.degree. F. Generally, the larger the size of the photomask plate, the more adhesive material is required for adhering the pellicle frame.
One method for removing pellicle frames is by using a small pry bar to pry the pellicle frame from the surface of the photomask plate. The pry bar has a curved end. The elbow of the curve rests on the surface of the photomask plate, and the end of the pry bar engages de-mount holes on the outside of the pellicle frame. The other end of the pry bar can then by used to apply force to the pellicle frame. This method works well with pellicle frames adhered with double-sided adhesive gasket tape. This method does not work well with pellicle frames attached using the solid adhesive gasket (SAG) material. Rather than crisply separating, as with traditional gasket tapes, the SAG material stretches and elastically snaps back. Thus, the pry bar removal is generally inadequate for use with SAG. Further, use of the pry bar provides an obvious opportunity to scratch or mar the surface of the photomask plate.
Another conventional method for removing pellicle frames is to heat the entire assembly, both the photomask plate and the pellicle frame, in a warm bath. This causes the adhesive material to melt and allow removal of the pellicle frame. However, when the pellicle frame is removed, the melted SAG material will often stream across the surface of the photomask plate. Any material remaining on the surface of the photomask plate clearly can destroy the usefulness of the photomask. Thus, while the bath method works to remove the pellicle frames, it is a relatively unclean and often leaves adhesive material across the plate surface.
A further method is to heat the pellicle frame through a device that engages the de-mount holes of the pellicle frame. This is somewhat better than the bath method, but the melted SAG material typically first releases from the warmer of two surfaces. By heating the pellicle frame, the pellicle frame is at a higher temperature than the photomask plate. Thus, when the pellicle frame is separated from the photomask plate, the SAG material remains on the photomask plate. Again, this is problematic because the photomask plate needs to remain clean and unblemished to be useful.
Therefore, it is desirable to provide a way to remove pellicle frames adhered using SAG and other adhesive materials that cleanly removes the pellicle frame without damaging the surface of the photomask plate or leaving adhesive material residue.